1. Field of the Invention
The present invention pertains generally to a sensor system, and more particularly to a system which can measure the range and direction to objects that are located in front of the sensor system.
2. Description of Related Art
Alternatives to the keyboard and mouse are being rapidly deployed in computers, smartphones, and tablets. The touch screen interface has gained traction in all three markets and dominates the smartphone and tablet market. The touch screen allows intuitive interfaces based on software buttons to be used and is especially ideal for small screens where the user's hand can easily traverse the entire screen. However, there are many situations where a touch screen is inappropriate or could be complemented by an interface that does not require the user to touch the screen.
Optical 3D imagers for gesture recognition suffer from large size and high power consumption. Their performance depends on ambient illumination and they generally cannot operate in sunlight. For example, the Microsoft Kinect 3D imaging system consumes 12 watts, has a volume of over 675 cm3, and cannot operate in sunlight. These factors prohibit use in portable electronics.
Ultrasound transmitters and receivers have used continuous wave signals to calculate the impulse response of a channel and to extract from this the user's gestures. However, use of continuous wave signals is susceptible to multipath interference, and requires extremely high dynamic range in the receive electronics. Multipath interference arises when transmitted waves reflect off several targets and arrive back at the receiver. If the waves have a slightly different path length, they can combine destructively, thereby canceling the return signal. The high dynamic range requirement arises because the ultrasound wave is attenuated as it travels to the target and back. When the wave returns, it is many times smaller than the transmitted signal. Generally there is significant leakage from the transmitter to the receiver, so the receiver must detect the faint echo in the presence of a large feedthrough component from the transmitter. This requires large dynamic range.
For gesture input to portable devices, it is desirable to build a system that has <1 cm3 size, <10 mW power consumption, and which can be used in a variety of environmental conditions. This invention provides an enabling technology to accomplish these goals.